In order to address disturbances such as variations in welding speed and length of wire extension, there has been conventionally known a technique of controlling a short circuit current during a short circuit period by changing a slope of a short circuit current and an inflection point of the short circuit current in a basic waveform of an optimal welding waveform.
For example, as shown in FIG. 9, there is known, in Patent Literature 1, an arc welding control method of welding an object to be welded by alternately repeating a short circuit period in which a short circuit is caused between a welding wire and the object to be welded and an arc period in which an arc is regenerated to cause an arc discharge that controls a slope of the basic waveform of the short circuit current by a two-step control. In FIG. 9, short circuit current It includes first tier slope J1 and second tier slope J2. Conventionally, second tier increasing slope J2 is adjusted to a “hard” K direction or a “soft” L direction from intermediate increasing slope J2 by adjusting a variable resistance of a slope adjuster knob. Further, by adjusting a current setter or an inflection point adjuster knob, short circuit current It at an inflection point between the first tier and the second tier is adjusted from intermediate point Ib to Ia greater than Ib or Ic smaller than Ib that are not shown in the drawing. Moreover, the welding current is freely controlled by a combination of these. Here, “soft” and “hard” respectively refer to a case in which a slope of short circuit current It of the basic waveform is small, and a case in which the slope of short circuit current It of the basic waveform is large.
By adjusting the slope adjuster knob of the short circuit current to “soft” and the inflection point adjuster knob to “large”, it is possible to stabilize an arc and relatively reduce an amount of sputter generation, whereby stable wielding to a zinc-coated steel plate and such can be carried out. Further, by adjusting the slope adjuster knob of the short circuit current to “soft” and the inflection point adjuster knob to “small”, it is possible to minimize the amount of sputter generation and to make suitable for high speed welding although susceptible to variations in wire extension. Moreover, by adjusting the slope adjuster knob of the short circuit current to “hard” and the inflection point adjuster knob to “large”, it is possible to most stabilize the arc to the disturbance although the amount of sputter generation increases and beads are high.
As described above, according to the conventional technique, such an adjustment is carried out by an operator manipulating the knob for adjusting the second tier slope of the short circuit current and the knob for adjusting the inflection point of the short circuit current.
In recent years, in the welding industry, in order to improve productivity, there has been an increasing demand for increasing the welding speed and addressing the disturbances such as the variations in the length of wire extension and a gap between objects to be welded. Increasing the welding speed increases manufacturing quantity per hour and will not cause a flip of the welding wire even when the variations in the length of wire extension or the gap generation occur, and it is possible to weld without any bead defect, sputter increase, or burn-through due to arc instability. This provides advantageous effects of increasing a yield ratio of the object to be welded and reducing the number of correction steps.
Generally, as the number of short circuits is increased in case of increasing the welding speed, a setting voltage is often set to be smaller than a typical optimal voltage (hereinafter referred to as a unitary voltage) by a few V. As used herein, the unitary voltage is a voltage suitable for welding and corresponding to a setting current set by the operator. If the welding speed is high, a molten pool is less likely to be formed under the arc, as compared to a case in which the welding speed is low. Accordingly, the number of short circuits is increased in order to improve a following capability of the molten pool. However, as this by contrast reduces the arc period, a size of a droplet at a tip end of the welding wire becomes small, and it becomes harder to melt the welding wire in the next short circuit as well as to open the short circuit.
As a result, a problem has been noted that, in the worst-case scenario, the arc becomes instable to cause a wire flip as the welding wire is not completely molten, thereby causing problems such as the bead defect, sputter increase, and lack of penetration. Accordingly, the conventional technique described above addresses the above problems by adjusting the slope of the short circuit current and the inflection point of the short circuit current.
However, according to the conventional technique, the adjustment of the increasing slope of the short circuit current and the adjustment of the inflection point of the short circuit current have to be carried out by the welding operator manipulating the knob at the same time as the adjustment of the setting voltage, and there has been a problem that it is difficult for the operator to carry out such adjustments.